@clean nodes stopped updating

[edreamleo]

First reported here.

Joe Orr: I'm going back and forth between Leo and Webstorm. (MacOS 10). Until today, when I made a change in a @clean file in Webstorm, Leo would pop up a message saying that the file has been changed and update its copy. That just stopped happening. Now Leo doesn't update the node unless I close and open the Leo file.

I'm not aware of any changes I made in my setup that could have caused this.

After it started happening I did the following:

1. Deleted my Leo install and reinstalled from git, version is now 5.5.
2. Verified that Webstorm is updating the file on the filesystem.
3. Tried deleting and recreating the @clean node.

Refresh from disk works, also, I do get a warning when I try to save changes in Leo version and target file has other changes.

[edreamleo]

Updates of both @clean and @file external files work for me on Windows 10.

Naturally, the updates only happen when the external file has been saved to disk.

[edreamleo]

This was a difficult to find problem with settings, a side effect of #262: Improve performance of check_for_changed_external_files.

@bool check_for_changed_external_files must be True to enable checkin in any .leo file.

0fb4cec improves traces in efc.on_idle to make clearer what is happening.